Electrostatic precipitator



Dec. 9, 1958 Y Y H. KLEMPERER l 2,863,523

ELECTRQSTATIC PRECIPITATOR Filed March 6, 1956 5 Sheets-Sheet 1 l NV ENTO R Hans Klemperer ATTO NEY Dec- 9, 1958 I H. KLEMPERER .2,863,523

ELECTROSTATIC PRECIPITATOR Filed1 March 6, 1956 l 3 Sheets-Sheet 2 4af-f .2 Flg. 5 43 INVENTOR .WM ZTORNEY Dfw-l 9, 1958 H. KLEMPERER2,863,523

ELECTROSTATIC FRECIPITATOR Filed March 6, 1956 3 Sheets-Sheet 3 INVENToRHans Klemperer ATTORNEY nited States Patent C) ELECTROSTATICPRECIPITATOR Hans Klemperer, Belmont, Mass., assignor to APRAPreciptator Corporation, New York, N. Y., a corporation of DelawareApplication March 6, 1956, Serial No. 569,759

11 Claims. (Cl. 183-7) The present invention relates to electrostaticprecipitators for the removal from combustion or other impure gases ofne solid particles or impurities and relates particularly to improvedmeans for automatically controlling the application of charging voltagesto the precipitator electrodes during the particle collecting andcleaning or discharge cycles of such precipitators.

The precipitator in which the invention is embodied eiects removal ofimpurities without interruption from a continuously flowing column ofany impure gases by electrostatic means incorporated in apparatusproviding an ionizing section or zone followed by a collecting sectionor zone in which the particles previously electrostatically charged inthe ionizing zone are deposited and collected on a suitable collectingsurface. The precipitator comprises a number of individual banks ofelectrodes arranged in collecting sections having a total crosssectional area for ow of gases greater than that required for flow ofthe gas column to be treated so that less than the total number of gaschannels provided are utilized at a given time while the remainder ofthe channels are momentarily in a cleaning zone outside the path of flowof the gas column in order that the collecting surfaces may be cleanedwithout interrupting the gas cleaning function of the apparatus as awhole.

In particular the invention contemplates apparatus of the kind describedin which means are provided for automatically regulating the voltageapplied to the charged electrode elements of the precipitator inaccordance with the operating conditions of a boiler, for example, withwhich the precipitator is associated as reected by the frequency offlashovers occurring in the precipitator as a whole, as well as theindividual electrode banks.

A salient feature of the present invention is that individual powersources are provided for each of the individual collecting sections orelectrode banks of the precipitator and a common regulating meanscontrols all of these power supplies in response to the frequency ofoccurrence of ashovers in the precipitator as a whole. Concurrently eachindividual electrode bank of the precipitator may have the chargingvoltage that is applied thereto separately regulated in accordance withthe frequency of occurrence of flashovers in the particular electrodebank.

In the drawings:

Figure l is a schematic view of a gas cleaning system incorporatingindividual power supplies with a common voltage regulating means for thevarious electrode banks in accordance with the present invention;

Figure 2 illustrates an alternative larrangement for part of the`control system illustrated in Figure 1;

Figure 3 is a schematic wiring diagram of the power supply and separatecontrol means for a single electrode bank;

Figure 4 is a schematic wiring diagram of a modied form ofthe inventionfor controlling a precipitator in ICC accordance with the frequency ofoccurrence of flashovers.

Referring now more particularly to Figure l, the reference character 10indicates a duct delivering gases containing impurities from a furnaceor other apparatus and 11 is a discharge duct for carrying away thecleaned gases. Between ducts 10 and 11 a stationary housing 12 islocated. For the purposes of this description it is assumed that thehousing 12 is cylindrical and its interior divided by radial partitionsinto a series of sector-like compartments housing the electrode banksand collecting sections of the cleaner. The banks include lower ionizingsections and upper collecting sections. In Figure 1 the numerals 13, 14,15 and 16 designate four out of the total of twelve, for example,individual electrode banks of the precipitator. Each compartment or bankcomprises a multiplicity of open ended gas channels of hexagonal crosssection and each of the gas channels is traversed longitudinally by acentrally located electrode. Current is supplied to each electrode bankthrough an individual feeder 20, 21, 22, 23, so that the electrodes maybe electrically charged.

The casing structure is formed to provide a chamber 24 to which the gasinlet 10 leads and communicating with the space in which the ionizingand collecting sections are located. Within this chamber 24 there islocated a rotatably mounted hopper 25 projecting at its lower endthrough a suitable sealed opening 26 in the casing structure, beingcarried by a suitable bearing and having an external discharge outlet27. At the upper end of the shellstructure a rotatably mounted hood 28is provided, which comprises a sector shaped wing providing a chamberhousing a cleaning element in the form of a pipe 29 rotatable with thehood 28 by means of the suitable gearing.l Pipe 29 is connected to asource of high pressure fluid, such as steam or air. The hood 28operates to isolate a compartment to be cleaned from the compartmentsthrough which gas is owing, the hopper 25 being maintained inregistration with the hood 28 to effect this separation at the lower endof the apparatus. It will be evident that as the hopper 25 and hood 28are rotated electrode banks in different compartments can besuccessively cleaned without interruption to the flow through theapparatus of the gas to be cleaned.

The foregoing precipitator structure is more fully de- -scribed in thepatent to Per Hilmer Karlsson, No. 2,582,- 133, dated January 8, 1952.

Each of the electrode banks 13, 14, 15, 16 has associated therewith anindividual power supply 30, 31, 32, 33, respectively, for supplying anelectrical charge to the electrodes of the bank through the wires 20,.21, 22, and 23. Although only four electrode banks are shown it is tobe understood that there are others in a complete precipitator and eachhas its individual power supply. Figure 3 illustrates the wiringarrangements of each of these power supplies.

Referring to Figure 3 the power supply for one of the electrode banksderives its energy from a three wire alternating electrical currentsource 40 to which the primary winding 41 of a power transformer 42 isconnected. The secondary 43 of the transformer is connected to arectifier 44 which converts the alternating current to direct currentand through the wire 20, for example, supplies a high voltage chargingpotential to the electrodes of the bank 13 in the electrostaticprecipitator. Connected in series with the primary windings 41 ofthepower transformer 42 are three reactors 46, 47, 48, whose excitingwindings 50, 51, 52, are energized from .a separate source 53 of currentthrough a rectifier 54. The primary windings 41 of power transformer 42also vhave aaeaeae:

connected in parallel therewith three other reactors 5S, 56, 57, whoseexcitation windings 60, 61, 62, are energized from a tertiary coil 63coupled to the reactor primary ofiy onek of the series reactors (e. g.48). Theexcita tion for the parallel reactors is supplied through arectifier 64 and: aI time constant modifying resistor 65, tol theexcitation. coils 60, 61, 62, of the parallel reactors 55, 56, 5'7'.

The excitation for the series reactors 46, 47, 43, 1s governed fromv anintermediate or control reactor 66 which serves to amplify theexcitation power needed. The control reactor 66 is so connected to therectifier 34 as to be' of the self excited type displaying a highamplification andi a very fast operating time. This self saturatingcontrol reactor consists of the combination of two separate reactorcomponents 67, 63, andv the rectifier 54. Introduction of this controlreactor 66 reduces the power level for control purposes from two..hundred fifty watts, for example, to less thanl ten watts. At this lowlevel electro-mechanical control relays as heretofore used can bedispensed with and all necessary switching for reducing or cutting offvoltage during and restoring it after the cleaning period may beperformed, can be synchronizedwith the cleaning apparatus of theprecipitator as disclosed in application, Serial No. 224,356, filed May3, 1951, now Patent No. 2,672,947 issued March 23, 1954.

As shown in Figure 3, the ground resistor 75 between power rectifier 44and ground is tapped and the voltage which corresponds to precipitatorcurrent is introduced into the control reactor excitation coils 76, 77,in a direction opposing the external excitation from a regulatedseparate power source 78. This is because one side of the reactor 66windings 76, 77, is connected to the direct current source 78 so as tohave the same polarity with respect to ground as the low voltage side ofthe power rectifier 44. Thus, the feedback circuit 80 has a degenerativeand a stabilizing effect; the current in the precipitator sector limitsitself by regulating the excitation of reactor 66 and hence the seriesreactors 46, 47, 48. The position of the slider 75A on resistor 75defines the amount of feedback which is to be allowed. The feedback isset so that a rise in current during flashover is hardly noticeable. Itis expected that due to the current limitation as derived from thefeedback circuit 80 most of the ashovers in the precipitator will beblown out by the high gas velocity. A further benefit derived from the:current stabilizing action of the feedback is a more stable performanceof the precipitator under varying boiler load conditions.

Circuit 80 is energized by a current carried by two opposing potentials,the constant voltage taken from source 78 and the varying voltagecarried by the varying precipitator current liowing through 75. Thecurrent through 75 thus causes a current in circuit 80 which varies ininverse relation, i. e. it rises if the current in 75 falls and falls ifthe current in 75 rises. Therefore the excitation 77 of the controldevice 67, 68 varies in inverse direction with the flow of current inthe precipitator and its acts to control this current in opposite sense.A rise in precipitator current causes the control device to counteractits rise. This counteraction of variations automatically performed bythe controlling device is described herein by the term degenerativefeedback.

The presence of the control reactor 66 considerably facilitates theextinction of flashovers. A flashover is a secondary short circuit and amanifests itself in a sudden breakdown of voltage (from 15,000 v. toabout 100 v.). Flashovers behave `differently according to their pointsof origin. Iff they originate from dusty spots, as on the electrodes,they are most persistent. Since a precipitator sector does not remainclean during the length of its operating cycle, it is expected that someflashovers may stay. Therefore, an additional extinction circuit isneeded and the trigger impulse for the extinction circuit is taken fromthe voltage breakdown.

In order that the voltage applied to the electrodesv of the variousbanks 13, 14, 15, 16, etc., may be regulated in response to thefrequency of occurrence of ashover in the precipitator as a whole, theground return leads S2, 83, 84,185, etc., of all of the power supplies30, 31, 32, 33 (as well as others not illustrated) are connectedtogether by a wire 86 and grounded at 87 through a common impedance 38as shown in Figure 1. Any flashover in any power supply, i. e. in thecoordinated electrode bank sector, will cause a transient voltagebuildup across impedance This transient voltage is conducted through acapacity 90 to a storage device 91. Capacitance 90 serves to keepconstant voltage drop across irnpedance 8S as caused by precipitatorionizing power away from storage device 91 and makes this storage devicedependent on flashovers only. The storage device 91 may be a thermal, anelectrostatic or a mechanical storage device for instance. A thermaldevice is shown consisting of a thermonegative resistance (thermistor)heatable by the current passing 90. The temperature and therefore theresistivity of the thermonegative resistance is consequently a functionof theA flashover frequency in the precipitator.

A separate power source supplies direct current through the rectifier101 to.` the excitation winding 102 of the control reactor 103 whosewindings 104 and 105 are supplied with current through the rectifier 106which is also connected to the power source 100. The output ofrec'tifier1fi6 constitutes the separate power source 78 for the powersupply 30 shown in. detail in Figure 3 and all of the other powersupplies 31, 32 and 33 as shown in Figure 1. Connected in parallel withthe excitation winding 102 of the reactor 103 is the thermo-sensitiveresistance (thermistor) 91. The thermistor 91 bleeds off a part of thecurrent which is supplied to winding 102 from the source 101- through afixed resistor 107 and an adjustable resistor 108.

Flashover currents from any of the power supplies 30, 31, 32 pass theinductors 88 to ground 87. The change in voltage across 33 is conductedthrough a coupling capacity 90 to a heater winding which heats thethermistor body of thermistor 91. Therefore the temperature of thethermistor body depends on the occurrence. of flashovers and not on thedirect current flowing through 88. As the body of thermistor 91 heats upit drains current away from excitation winding 102 of reactor 103 bymeans of which the current flowing thro-ugh reactor coils 104 and 105and the coordinated rectifier 106 is reduced and the control reactor 103common to the power supplies 30, 31, 32 gets less excitation, the resultbeing that the power output of all supplies is simultaneously reduced.As boiler conditions vary, the flashover frequency in the precipitatorwill vary and the power output of the power supplies will automaticallybe increased or decreased by variation of the common voltage controllingall individual power supply control reactors.

An electrostatic storage device as an alternate is shown in Figure 2wherein the points or terminals 92, 93, 94, 95 correspond to the similarterminals in Figure l. The voltage impulse passing capacitance 90 isrectified at 110 and stored on a capacitor 111. The energy is slowlybled off or dissipated at a rate determined by the size of a resistor 12which thus corresponds to the natural cooling off of the thermal deviceshown in Figure l. The voltage stored by the capacitor-111 applied toreduce a constant negative bias on the grid 113 of an electronic tube114. The plate resistance of this tube is therefore a function of theflashover frequency in the precipitator and this governs the voltageapplied by the power units 30 to 33 to the electrode banks.

The common power supply regulator of Figure 1 Will operate only if allor the majority of power supplies start flashing. It will ordinarily notbe affected by an increased fiashover rate in a single power supplybecause the integrator 8S is set to such sensitivity that 12 timeshigher impulse rate would be needed to properly excite the storagedevice 91. A high flashover rate in a single power supply, i. e. in thecoordinated electrode bank, excites sufliciently its individualregulator 75 (Figure 3) which is adjusted to respond to these impulsesonly. The relative inertias of the individual regulators with respect tothe inertia of the common regulator are adjustedadjustments are made byvarying the respective thermal or electrical capacities-so thatindividual differences in ashover rates between the sectors adjustthemselves before the common regulator responds.

Control of voltage applied to an individual electrode bank as theflashover frequency in the electrode bank rises is shown in Figure 3.The heating winding 72 of the thermistor 73 for bank 30 is connected tothe related ground resistor 75 through a wire 79 on one side and on theother through the same resistor in adjustable manner through a wire 81A.Since the thermistor 73 is connected by the wire 70 into the circuit 74of the activating windings 76 and 77 of the reactor 66, the heating ofthe thermistor 73 results in bleeding current from these energizingwindings and reduces the power supplied by the reactor 54 to the powersupply transformer 42 and rectifier 44 which supplies the precipitatorsector 13. The tube circuit of Figure 2 could also be utilized for theindividual power supplies for the electrode banks in place of thethermistor 73.

In Figure 4 a thermistor 120 which reflects the frequency of flashoversin any of the precipitato-r sections 13, 14, 15, 16 is arranged totransmit a control signal through the wires 121 and 122 to a speedcontrol device 123 which acts upon a drive motor 124 to regulate thespeed of rotation of the cleaning nozzle 29 so that as the rate ofashovers increases, the speed of the cleaning nozzle is accelerated withthe result that the cleaning cycle for the precipitator occurs morefrequently.

As described in detail with reference to Figure l a resistance 88 isprovided in the common ground return line of all power supplies 30, 31,32, 33, etc. Every ashover in any electrode bank 13, 14, 15, 16, etc.,will appear as a voltage pulse across the resistor 88. This signal ispassed by means of condensor 90 to an integrating device, thermal,electrostatic or mechanical. If a certain level is reached in theintegrating device 120 the speed control 113 of the precipitator isinuenced, by relay or tube control, and speeds up the drive motor 114for the cleaning apparatus. Resetting is eiected by cooling down ordischarge of the integrating device when ashovers have subsided.

What I claim is:

l. In an electrostatic precipitator; energy storage means responsive totransient voltage uctuations in the precipitator produced by ashoverstherein; means associated with said energy storage means for dissipatingthe energy stored therein at a predetermined rate; and means responsiveto the residual energy stored in said energy storage means forcontrolling the operation of said precipitator.

2. In an electrostatic precipitator; having a bank of electrodes,electrical supply means for charging the electrodes of said bank, andcontrol means associated with power supply for regulating the powersupplied to said bank; energy storage means responsive to transientvoltage iluctuations in the precipitator produced by flashovers therein;means associated with said energy storage means for dissipating theenergy stored therein at a predetermined rate; and means responsive tothe residual energy stored in said energy storage means for operatingsaid control means to vary the output of said power supply means.

3. In an electrostatic precipitator having a group of separate banks ofelectrodes, a plurality of power units each individual to one of saidelectrode banks for supplying a high voltage current thereto, andindividual control means in each power supply unit controlling thecurrent supply to the related electrode bank independently of otherelectrode banks; a common regulating means for said control means; acommon circuit connecting all of said power supplies to an electricalground; means responsive to transient voltage fluctuations in saidground circuit for measuring the frequency of occurrence of flashoversin said group of electrode banks as a whole; and means responsive tosaid measuring means and acting on the said fcornmon current regulatingmeans that is associated with said group of electrode banks forproportionately varying the output of all said power unitssimultaneously.

4. In an electrostatic precipitator having a group of separate banks ofelectrodes, a plurality of power units each individual to one of saidelectrode banks for supplying a high voltage current thereto, andindividual control means in each of said power supply units separatelycontrolling the current supply to the related electrode bank; a commonregulating means for said control means; a common circuit `connectingall of said power supplies to an electrical ground; energy storage meansresponsive to the transient iluctuations in said ground circuit producedby ashovers in said group of electrode banks as a whole; means fordissipating the stored energy at a predetermined rate; `and meansresponsive to the energy stored in said energy storage means foroperating said common current regulating means.

5. In an electrostatic precipitator having a group of separate banks ofelectrodes, a plurality of power units each individual to one of saidelectrode banks for supplying a high voltage current thereto, andindividual control means in each power supply unit separatelycontrolling the current supply to the related electrode bankindependently of other electrode banks; a common regulating means forsaid control means; a common circuit connecting all of said powersupplies to an electrical ground; electronic means for controlling saidregulating means; and electrical means associated with said commonground circuit for making the output of said electronic means responsiveto the transient voltage uctuations in said ground circuit produced byflashovers in said group of electrode banks as a whole.

6. In an electrostatic precipitator having a group of separate banks ofelectrodes, a plurality of power units each individual to one of saidelectrode banks for supplying a high voltage current thereto, andindividual control means in each of said power supply units and eachseparately controlling the current supply to the related electrode bankindependently of other electrode banks; a common regulating means forsaid control means; a common circuit connecting all of said powersupplies to an electrical ground; a thermistor for controlling saidregulating means; and electrical means associated with said commonground 'circuit for mak-ing the temperature of said thermistorresponsive to the transient voltage fluctuation in said ground circuitproduced by lashovers in said group of electrode banks as a whole.

7. In an electrostatic precipitator having a group of separate banks ofelectrodes, a plurality of power units each individual to one of saidelectrode banks for supplying a high voltage current thereto, andindividual control means in each power supply unit controlling thecurrent supply to the related electrode bank independently of otherelectrode banks; a common regulating means for said control means; acommon circuit connecting all of said power supplies to an electricalground; an impedance in said circuit; means responsive to transientuctuations in the voltage drop across said impedance for measuring thefrequency of occurrence of llashovers in said group of electrode banksas a whole; and means responsive to said measuring means 'and acting onthe said common current regulating means that is associated with thecontrol means for the power units of said group of electrode banks forproportionately varying the output of all said power unitssimultaneously.

8. In an electrostatic precipitator having a bank of electrodes, anelectrical power supply unit for charging said electrode bank; means insaid power supply unit for controlling the current supplied to said bankof electrodes; an electrical grounding circuit for said electrode bank;means responsive to transient voltage uctu'ations in said ground circuitfor measuring the frequency of occurrence of ashovers in said bank ofelectrodes; and means responsive to said measuring means and acting onsaid current control means for said bank to proportionately vary theoutput of said power unit in a direction to reduce said transientvoltage fluctuations.

9. In an electrostatic precipitator having a plurality of separateelectrode banks; means operable to clean said electrode banks incyclically repeated sequential relation; :a drive motor for saidcleaning means; speed regulating means for said motor; and meansresponsive to transient voltage fluctuations in said precipitatorproduced by flashovers for measuring the frequency of occurrence ofHashovers in said plurality of electrode banks as a whole acting uponsaid motor regulating means for varying the rate of cleaning of saidelectrode banks.

10. In 'an electrostatic precipitator having a bank of electrodes forionizing entrained particles in a gas stream, electrical power supplymeans for charging said electrode bank; means in said power supply meansfor controlling the current supplied to said bank of electrodes;collecting surfaces for deposition of said particles; an electricalground circuit for said surfaces; regulable means operable cyclicallyfor cleaning said collecting surfaces; means responsive to transientvoltage fluctuations in said ground circuit for measuring the frequencyof occurrence of flashovers in said bank of electrodes; and meansresponsive to said measuring means and acting on said current'controlmeans for said electrode bank to proportionately vary the output of saidpower unit in a direction to reduce said transient voltage fluctuations.

1.1. "In an electrostatic precipitator having separate banks ofelectrodes, individual power units for'said ele'ctrode banks forsupplying a high voltage current thereto, and individual control meansin each power supply unit controllingthe current supply to the relatedelectrode bank independently of other electrode banks; a commonregulating means for said control means; a common circuit connecting allof said power supplies to an electrical ground; means responsive totransient voltage fluctuations in said ground circuit for measuring thefrequency of occurrence of ashovers in said precipitator as a whole;means responsive to said measuring means and acting on the said commoncurrent regulating means that is associated with all said electrodebanks for proportionately varying the output of all power units of thepricipitator simultaneously; individual energy storage means for eachelectrode bank responsive to transient voltage fluctuations produced inthe related electrode bank by ashovers therein; separate meansassociated with each energy storage means for dissipating the energystored therein at a determined rate; and individual means for eachelectrode bank responsive to the residual energy stored in the relatedenergy storage means for operating the control means in the power unitfor the particular bank to Vary the output of said power unitindependently of those for other banks.

References Cited in the le of this patent UNITED STATES PATENTS2,642,149 Backer et al. June 16, 1953 FOREIGN PATENTS 149,367 AustraliaDec. 10, 1952 705,604 Great Britain Mar. 17, 1954

